This invention was made with Government support under Contract No. DE-FG02-86ER13511 awarded by the Department of Energy. The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

This invention relates to the compositions of matter useful as catalysts, to a method for preparing these catalysts and to a method for polymerization utilizing the catalysts.

The use of soluble Ziegler-Natta type catalysts in the polymerization of olefins is well known in the prior art. In general, such systems include a Group IV-B metal compound and a metal or metalloid alkyl cocatalyst, such as aluminum alkyl cocatalyst. More broadly, it may be said to include a mixture of a Group I-III metal alkyl and a transition metal complex from Group IVB-VB metals, particularly titanium, zirconium, or hafnium with aluminum alkyl cocatalysts.

First generation cocatalyst systems for homogeneous metallocene Ziegler-Natta olefin polymerization, alkylaluminum chlorides (AlR2Cl), exhibit low ethylene polymerization activity levels and no propylene polymerization activity. Second generation cocatalyst systems, utilizing methyl aluminoxane (MAO), raise activities by several orders of magnitude. In practice however, a large stoichiometric excess of MAO over catalyst ranging from several hundred to ten thousand must be employed to have good activities and stereoselectivities. Moreover, it has not been possible to isolate characterizable metallocene active species using MAO. The third generation of cocatalyst, B(C6F5)3, proves to be far more efficient while utilizing a 1:1 catalyst-cocatalyst ratio. Although active catalyst species generated with B(C6F5)3, are isolable and characterizable, the anion MeB(C6F5)3⊖, formed after Me⊖ abstraction from metallocene dimethyl complexes is weakly coordinated to the electron-deficient metal center, thus resulting in a drop of certain catalytic activities. The recently developed B(C6F5)4⊖ type of non-coordinating anion exhibits some of the highest reported catalytic activities, but such catalysts have proven difficult to obtain in the pure state due to poor thermal stability and poor crystallizability, which is crucial for long-lived catalysts and for understanding the role of true catalytic species in the catalysis for the future catalyst design. Synthetically, it also takes two more steps to prepare such an anion than for the neutral organo-Lewis acid.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the subject invention to prepare and utilize a new class of olefin polymerization catalysts.

A further object of the subject invention is a catalyst which permits better control over molecular weight, molecular distribution, stereoselectivity, and comonomer incorporation.

Another object of the subject invention is a Ziegler-Natta type catalyst system which reduces the use of excess cocatalyst and activates previously unresponsive metallocenes.

These and other objects are attained by the subject invention whereby in one embodiment, a strong organo-Lewis acid, such as perfluorobiphenylborane (PBB) is utilized as a highly efficient cocatalyst for metallocene-mediated olefin polymerization and as a catalyst for a ring opening polymerization of THF. PBB can be synthesized in much higher yield than B(C6F5)3 and the anion generated with PBB is non-coordinating instead of weakly coordinating as in the case of B(C6F5)3. Thus, the former exhibits higher catalytic activities and can activate previously unresponsive metallocenes. The catalytically active species generated with PBB are isolable, X-ray crystallographically characterizable instead of the unstable, oily residues often resulting in the case of B(C6F5)4⊖. In addition, PBB exhibits even higher catalytic activities in most cases.

In one embodiment of the subject invention a strong organo-Lewis acid, such as perfluorobiphenylborane (PBB), is utilized to synthesize stoichiometrically precise, isolable/crystallographically characterizable, highly active “cation-like” metallocene polymerization catalysts. The biphenyl groups of PBB may be connected to the boron at the meta, para, or ortho position.

As a specific example of the above, the reaction of PBB with a variety of zirconocene dimethyl complexes proceeds rapidly and quantitatively to yield, after recrystallization from hydrocarbon solvents, the catalytic complex of Eq. 1.

Such catalytic complexes have been found to be active homogeneous catalysts for α-olefin polymerization and, more particularly, the polymerization, copolymerization or oligopolymerization of ethylene, α-olefins, dienes and acetylenic monomers, as well as intramolecular C—H activation.

The cocatalyst of the subject invention may be referred to as BR′R″2, where B=boron; R′ and R″ represent at least one and maybe more fluorinated biphenyls or other polycyclic groups, such as naphthyl. Two of the biphenyls may be substituted with a phenyl group. Both the biphenyls and the phenyl groups should be highly fluorinated, preferably with only one or two hydrogens on a group, and most preferably, as in PBB with no hydrogens and all fluorines.

BRIEF DESCRIPTION OF THE DRAWINGS

The cocatalyst system of the subject invention can be better understood with reference to the drawings wherein:

FIG. 1 is a structural depiction of PBB;

FIG. 2 is a reaction pathway for the synthesis of PBB;

FIG. 3 shows the reaction pathway for a catalyst system according to the subject invention;

FIG. 4 shows the reaction pathway for a second catalyst system according to the subject invention;

FIG. 5 shows the reaction pathway for a third catalyst system according to the subject invention;

FIG. 6 shows the reaction pathway for a fourth catalyst system according to the subject invention; and

FIG. 7 shows the reaction pathway for a fifth catalyst system according to the subject invention.

DETAILED DESCRIPTION OF THE INVENTION

The reaction of perfluorobiphenylborane with a variety of zirconocene and other actinide or transition metal dimethyl complexes proceeds rapidly and quantitatively at room temperature in noncoordinating solvents to yield, after recrystallization, complexes. This catalyst activation reaction may be used in the polymerization, copolymerization, oligomerization and dimerization of α-olefins. In addition, the catalyst of the subject invention may be used in conjunction with aluminum alkyls, aluminum aryls, (AlR3, R=Et, Me, Ph, naphthyl) or methyl alumoxane (Al(CH3)O)n for increased polymer yields.

PBB (FIG. 1) has been synthesized in quantitative yields of 91 % as compared to the 30-50% yields experienced with B(C6F5)3, currently a very important Lewis acidic cocatalyst in industry (FIG. 2). The Lewis acidity of PBB has been shown to be much greater than that of B(C6F5)3 by comparative reactions of Cp*2ThMe2 with B(C6F5)3 and PBB (Cp*=C5Me5). The former reagent does not effect Me⊖ abstraction, while the latter gives the catalyst shown in FIG. 3. The reaction of PBB with a bis-Cp type of dimethyl zirconocenes forms a dinuclear methyl-bridged zirconocene cation such as

(1:1 or 2:1)

where

Cp=C5H5

Cp=C5H3Me2 or

Cp=C5Me5

and a hydride-bridged analog such as

where

Cp=C5H5 or

Cp=C5H3Me2

More particularly, reaction of PBB with group 4 and Th methyls proceeds cleanly to yield cationic complexes such as set forth below.

For ethylene polymerization, catalytic activities of dinuclear cations generated from PBB are greater than those of monomeric cations generated from B(C6F5)3 presumably because (MePBB)⊖ is a non-coordinating anion as compared to the weakly coordinating anion MeB(C6F5)3. The dinuclear cations have also been found to catalyze the rapid ring-opening polymerization of THF to produce poly(tetrahydrofuran), an important thermoplastic elastomer and artificial leather. Monomeric zirconocene cations have also been generated in situ by the reaction of Cp2ZrMe2 and PBB at 60° C.:

where Cp=C5H5, C5H3Me2, or C5Me5, or

These attempts show very high activities for olefin polymerization, and identify (MePBB)⊖ to be a truly non-coordinating anion. The polymerization data with metallocene cations having various anions are summarized in Table 1.

Other types of cationic metallocene catalyst systems can also be created with PBB. Metallocene cations of mono-Cp type (FIGS. 4 and 5) have been formed by the reaction of mono-pentamethyl Cp trimethyl group IV complexes with PBB. These are very good syndiospecific styrene polymerization catalysts. Constrained geometry types of zirconocene and titanocene cations such as those in FIG. 6 where m=Zr, Ti, are readily produced by the reaction of the corresponding dimethyl metallocenes with PBB. They are highly naked cations and much more active catalysts than those generated with B(C6F5)3.

EXAMPLE 1

Synthesis of Perfluorobiphenylborane (PBB)

n-Butyllithium (1.6 M in hexanes, 25 mL, 40 mmol) was added dropwise to bromopentafluorobenzene 18.0 g, 9.1 mL, 72.9 mmol) in 100 mL of diethyl ether over a cold-water bath. The mixture was then stirred for a further 12 h at room temperature. Removal of solvent followed by vacuum sublimation at 60-65° C./10−4 torr gave 12.0 g of 2-bromononafluorobiphenyl as a white crystalline solid: yield 83.3%. The dangerous and explosive nature of C6F5Li-ether solutions in this preparation can be avoided by (a) the use of excess of C6F5Br, (b) slow addition of n-butyllithium, (c) frequent change of the cold water bath, or use of a continuous flowing cold water bath.

5(a) Cp=C5H5. In a J-Young NMR tube, a small amount of a mixture of Cp2ZrMe2 and PBB (1:1.2 molar ratio) was dissolved in C6D6). The NMR tube was then put in an NMR probe and heated at 60° C. After 0.5 h, 1H NMR revealed the above monomeric species formed. The same structures were obtained by the reaction of the product of Example 3 with excess of PBB at 60° C. for 0.5 h. In a real polymerization test, these species were also generated in situ by mixing Cp2ZrMe2 and PBB at 60° C. for 0.5 h. 1H NMR (C6D6, 60° C.) for: δ5.70 (s, 10H, C5H5), 0.14 (s, 3H, Zr—CH3), −0.85 (s, br, 3H, B—CH3). The 19F NMR is similar to that of the corresponding dinuclear species of Example 3 (Cp=C5H5).

5(c) Cp=C5Me5 The same procedure of Example 5(a) was used to prepare this species. In the polymerization test, the following was observed: 1H NMR (C6D6, 60° C.): δ1.61 (s, 30H, C5Me5), 0.13 (s, 3H, Zr—CH3), −0.86 (s, br, 3H, B—CH3). 19F NMR is similar to that of the corresponding dinuclear species of Example 3, Cp=C5Me5.

The reaction was conducted in a 250 mL flamed round bottom flask attached to a high vacuum line. The flask was equipped with a large magnetic stirring bar and a straight-bore high vacuum stopcock. The exterior connecting tube of the stopcock (Ca. 10 mm in length) is sealed with a new serum cap. The reaction vessel is then evacuated for several hours, back-filled with inert gas (Ar), the stopcock closed, and the reaction flask reevacuated. A measured amount of a nonpolar solvent such as benzene or toluene is vacuum transferred into the flask. Gaseous ethylene is admitted to the reaction flask through the purification column. The gas pressure is continuously maintained at 1 atm. Rapid stirring of the solution is initiated and after several minutes (to allow the saturation of the solvent with ethylene), the stopcock is opened and a small aliquot of catalyst solution (in the same solvent as used for the reaction) is injected by a gas-tight syringe just above the rapidly stirring solution through a serum cap (the syringe needle had been flattened so that the catalyst solution exits in a fine spray). Solid polyethylene is formed immediately. The reaction is quenched after a certain amount of time by injecting methanol through the serum cap on the stopcock. The solid polyethylene was collected by filtration, washed with methanol and then dried under vacuum at 100° C. Copolymerization may occur with the addition of a second monomer such as another α-olefin.

Ethylene polymerizations were carried out at room temperature in 250-mL flamed, round-bottom flasks attached to a high-vacuum line. In a typical experiment, a solution of each of the catalysts of Example 3 in 2 mL of toluene was quickly injected using a gas-tight syringe equipped with a spraying needle into respective rapidly stirred flasks containing 100 mL of toluene which was pre-saturated under 1 atm of rigorously purified ethylene. In the case of the catalysts prepared in Example 3, the catalyst solution was generated in situ by mixing Cp2ZrMe2 and PBB in 2 mL of toluene after aging for 0.5 h at 60° C., and then quickly injected into respective flasks under an ethylene atmosphere using a pre-warmed gas-tight syringe. The polymerization was quenched with acidic CH3OH after a short time period (10-60 s) at which point voluminous quantities of polyethylene precipitated out. The respective polymeric products were collected by filtration, washed with methanol and dried under high vacuum to a constant weight.

EXAMPLE 9

Ring-Opening Polymerization of THF

A small amount of [(C5H3Me2)2(Me)Zr—Me—Zr(Me)(C5H3Me2)2]⊕ (MePBB)⊖ was loaded into a J-Young NMR tube and THF-d8 was then vacuum-transferred into the tube. The mixture was slowly warmed to room temperature and left for several hours. The solid polymer formed in the tube was shown to be polytetrahydrofuran by 1H analysis.

EXAMPLE 10

Propylene Polymerization

This reaction is carried out in a 100 mL quartz Worden vessel equipped with a magnetic stirring bar, a pressure gauge and a stainless steel o-ring assembly attached to a high vacuum line. In a typical experiment, the reaction vessel is flamed and then pumped under high vacuum for several hours, filled with inert gas and brought into a glove box. A measured amount of catalyst is added into the vessel. On the high vacuum line, a measured amount of the solvent and propylene are condensed in at −78° C. The reaction apparatus is sealed off and warmed to the desired temperature. During the polymerization process, the reaction tube is immersed in a large amount of tap water (20-25° C.) or ice water (0° C.) to help dissipate the heat produced from the polymerization and keep the temperature constant. The progress of the polymerization reactions is monitored through observance of the pressure change. After the reaction is finished (pressure drops to zero psi), the resulting oily liquid is removed from the vessel, washed with methanol and water and dried under vacuum at 90-100° C. for ten hours to result in a colorless oil.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments and equivalents falling within the scope of the appended claims.

Various features of the invention are set forth in the following claims.